Dispelling the myth of bipolar glaciation 41 million years ago

August 30, 2007

Large continental ice sheets did not exist in both hemispheres around 41 million years ago during the warmer-than modern conditions of the time.

This is the finding of scientists from the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton (NOCS), reported in Nature.

The Eocene epoch (55 to 34 million years ago) was the last interval of sustained global warmth in Earth's history, a likely consequence of atmospheric carbon dioxide levels much higher than today. It has been known for some time that, at the end of the Eocene, ice sheets on Antarctica first expanded to close their modern size. However, in a recent controversial move, it was proposed that, despite the high global temperatures of the time, very large ice sheets existed 8 million years earlier, not just on Antarctica but also in the Northern Hemisphere.

New findings from NOCS researchers show that, if ice sheets did exist during the controversial interval they must have been small and would have been easily accommodated on Antarctica with no need to invoke Northern Hemisphere glaciation. This result is more in keeping with other geological records and climate model results suggesting that the threshold for ice sheet inception would have been crossed earlier in the Southern Hemisphere than in the Northern Hemisphere because the South Pole has a continent sitting over it (Antarctica) while the North Pole has an ocean (the Arctic).

The NOCS group also identifies a short-lived event immediately preceding the controversial interval during which ocean temperatures briefly increased, the deep ocean became more acidic and the carbon cycle was perturbed by the contribution of isotopically light carbon to the ocean/atmosphere system. This finding hints at the operation of carbon cycle processes common to those thought responsible for the famous transient extreme warming events that occurred between 50 and 55 million years ago, providing a focus for future work aimed at better understanding climate-carbon cycle feedbacks.

Kirsty Edgar, Dr Paul Wilson and Philip Sexton of the University of Southampton's School of Ocean and Earth Science, based at NOCS, used stable isotope analysis of fossil shells of foraminifera (microscopic marine organisms) and bulk sediment from deep-sea sediments to generate a record of climate change and estimate potential global ice volumes in the Eocene. Sediment cores were taken in the tropical Atlantic Ocean by the Ocean Drilling Program (ODP).

Source: University of Southampton

Explore further: Mapping land claimed by sea level rise

Related Stories

Mapping land claimed by sea level rise

August 20, 2015

The New Jersey shoreline that sea birds wandered during the last ice age is about 90 miles east of today's beaches, tens of meters beneath the sea floor. As the ice melted, sea level gradually rose and flooded the coastal ...

Rosetta hits 'milestone' in comet's run past Sun

August 13, 2015

The European space probe Rosetta captured a range of scientific data Thursday as it trailed an ancient comet past the Sun which could help scientists better understand the origins of life on Earth.

Recommended for you

Earth's mineralogy unique in the cosmos

August 26, 2015

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.